Interspecific Aggression - Fighting Fruit Flies

​A fundamental question in the field of behavioral ecology is: Why do animals fight? Evolutionary theory tells us that aggression can readily evolve because when resources are limited natural selection will favor aggressive individuals. This prediction holds unless the cost of aggression outweighs the benefit of procuring resources. But, what are the factors that influence the level of aggression between individuals of the same species (conspecifics) versus members of different species (heterospecifics)? Darwin proposed that closely related species are the most likely to compete with one another because they utilize the same types of resources, such as food and territory (i.e., the limiting similarity hypothesis). Despite this longstanding prediction, there is relatively little data on aggression behavior between species, with most of the research focusing on aggression within a species. Thus, while we know that individuals of different species compete for resources, and interspecific aggression is widespread in the animal kingdom, we don’t know how the level of competition for a given resource influences the level of aggression within versus between species.

We are addressing this gap in knowledge by comparing the levels of aggression within and between species of Drosophila flies, of both closely related and distantly related species. We have found that flies discriminate between members of their own species and individuals of a different species in aggressive interactions. Interestingly, the level of aggression depends on genetic relatedness and whether or not the competing species mate with one another. Check out our forthcoming manuscript on bioRxiv here. Also, check out our sample videos below to watch these fighting fruit flies in action!

This first video (above) shows males of distantly related Drosophila simulans (white dot on thorax) and Drosophila ananassae facing off in our multi-species aggression arena. Notice how nearly all aggressive encounters occur between members of the same species.​​

In contrast to the first video, this second video shows males of closely related Drosophila melanogaster (white dot on thorax) and Drosophila simulans. Notice how there are aggressive encounters between members of the opposite species in addition to members of the same species.